The present invention relates to the field of component assemblies, comprising at least one fixing device which is provided with a crimping ring. The invention more specifically relates to positioning a device for protecting the fixing device against the risks linked with lightning strikes.
The invention is very preferably used for assemblies for aircraft.
The fixing of non-metal components can be carried out with devices of the type comprising, on the one hand, a fixing element which is provided with a rod having a head and, on the other hand, a crimping ring. Using such crimped fixing devices, the components are clamped between the head and the crimping ring in order to carry out the plating thereof.
In particular for aeronautical applications, it is advantageous to protect the assembly against the risks linked with lightning strikes. This is because, when an arc of lightning strikes the head of the fixing element, an internal sparking can be seen between the rod of the fixing element and the non-metal components which are clamped between the head and the crimping ring. This sparking corresponds to the transfer of the current between the fixing device and these same components. The sparking leads to heating of the air in the zone of the bore of the components, possibly resulting in a release of hot gases at the side of the crimping ring. This phenomenon is known as “outgassing.”
In order to reduce the risks linked with such a release of hot gases, there is provision in the prior art for a protection device to be fitted which covers the portion of the fixing device located at the side of the crimping ring. Such a protection device delimits a confinement cavity into which any hot gases which are discharged can be introduced when lightning strikes the head of the fixing element. Consequently, the hot gases may remain confined in the cavity, thus protecting the surrounding elements which may be sensitive to these hot gases, for example, elements which are sensitive to heat.
The protection device is generally in the form of one or more caps which cover the portion of the fixing device located at the side of the crimping ring. These are generally two caps which are fitted one in the other with a sealing material placed in the space which separates those two caps. In a state applied and pressed against the non-metal component which receives the crimping ring, the protection device releases a portion of the sealing material which forms a sealed joint between the caps and the relevant component around the fixing device. The confinement, cavity can then be completely tight for better retention of the hot gases.
With caps which cover the portion of the fixing device including the crimping ring, the protection device also allows the risks of any spark to be limited between the crimping ring and the surface of the non-metal component against which this ring is in abutment and in contact. This phenomenon, which is also capable of being brought about in the region of the ring when the head of the fixing element is struck by lightning, is known as “thermal sparking.”
Satisfactory fitting of the protection device on the assembly requires above all correct positioning thereof relative to the fixing device which it covers. In particular it is important that the entire periphery thereof is pressed against the component to be fixed, around the fixing device.
In this regard, in order to ensure guiding of the protection device when it is placed around the fixing device, it has been envisaged to use the external lateral surface of the crimping ring as a guiding component. Nevertheless, after the crimping operation, the ring has a deformed geometry resulting from the creep of material brought about by this same crimping operation. Generally, the deformation seen is generated in the region of the end of the ring in contact with the component to be clamped, this end being able to be in the form of a crimping flange.
The deformed ring, although it provides satisfactory clamping, can be found to be ineffective in ensuring the guiding required for the protection device. It should further be noted that this risk is increased when an inclination exists between the axis of this crimping ring and the normal relative to the surface of the non-metal component against which this ring is in abutment. This is because, under these circumstances, the creep of material within the ring is more significant during, the crimping operation.
Taking, the above into account, the current solution involves the problem of the ability to repeat the operation for positioning the protection device.